Mammals characteristics include numerous adaptations that enable them to survive in a wide range of environments. They live in nearly every habitat around the globe, from frigid polar regions, to turbulent seas, to dense tropical forests. Modern mammals range in stature from tiny field mice to massive whales and although various species may look drastically different, all mammals still share a unifying set of characteristics.

Some mammal characteristics—such as their hair, mammary glands, and three specialized middle-ear bones—are shared by no other groups of animals. Here we'll explore key facts and information about mammals so we can better understand important mammal characteristics.

Hair Hair is one of the characteristics of a mammal that is unique to mammals—no other animals have true hair and all mammals have hair covering at least part of their body at some time during their life. An individual hair consists of a rod of cells that are reinforced by a protein known as keratin. Hair grows from skin cells called follicles. Hair can take on several different forms including thick fur, long whiskers, defensive quills or fearsome horns. Hair serves a variety of functions for mammals. It provides insulation, protects the skin, serves as camouflage and provides sensory feedback.

Some mammals have thick coats of fur that consist of two layers, a soft underfur and a coarse protective outer fur. Sea otters, for example, have this type of two-layered fur. In fact, sea otters have one the thicket coats of fur of all mammals, with more than 100,000 individual hairs per square centimeter. Since sea otters lack a layer of insulating blubber, they must compensate by having fur with superior insulation power. Cetaceans, in contrast, have a thick layer of insulating blubber and therefore have lost most of their hair over the course of their evolution. Some whales only have hair during their early development, while others retain sparse patches of hair on their chin or upper lip.

Mammary Glands Mammals nurse their young with milk produced by mammary glands. Mammary glands, like hair, are a uniquely mammalian trait. Though present in both males and females, in most mammal species mammary glands only fully develop in females. The exception to this rule is the male Dayak fruit bat, which has mammary glands that produce milk to feed its young.

Mammary glands are modified and enlarged sweat glands that consist of ducts and glandular tissues that secrete milk through nipples. Young mammals obtain milk from their mother by feeding from her nipples. The milk provides the young with much needed protein, sugars, fat, vitamins and salts.

Not all mammals have nipples. Monotremes, which include echidnas and the platypus, diverged from other mammals early in their evolution. Monotremes lack nipples and instead secrete the milk produced by their mammary glands through ducts in their abdomen.

Birds (Aves) are a diverse group of vertebrates that evolved from reptiles during the Mesazoic Era about 150 million years ago. Today, an estimated 300 billion birds belonging to more than 9000 species inhabit virtually every terrestrial habitat on the planet. There are even many species of birds that are at home in the water as skilled swimmers and divers. Birds range in size from the massive ostrich to the minute bee hummingbird. They have diversified into a wide variety of forms.

Birds possess distinct characteristics that make them one of the most distinguishable group of vertebrates. The following characteristics are unique to birds. Among these are:

·         feathers - provide insulation and enable flight; feathers are modifications of a bird's epidermis (outer skin)

·         bills - birds do not possess teeth or the heavy jawbones seen in other vertebrates; instead, birds have a pair of toothless mandibles covered with a horny sheath of keratin (also called ramphotheca).

·         furcula - also known as the 'wishbone', the furcula is a bone located in the bird's chest that prevents compression of the chest cavity during the downstroke of a wingbeat.

Birds also exhibit the following characteristics:

·         Fused bones in pelvis, feet, hands, and head

·         Lightweight bones (bones that are either hollow or spongy/strutted)

·         No teeth or maxillary bones of the jaw (reduces anterior weight)

·         Endothermic

·         Possess a four-chambered heart and in general exhibit high metabolic rates

·         Produce large, richly provisioned external eggs

·         Adept navigational abilities in many species

·         Extraordinary communication and song production

 (http://animals.about.com/od/birds/p/birds.htm)

Amphibian (class Amphibia),  any member of the group of vertebrate animals characterized by their ability to exploit both aquatic and terrestrial habitats. The name amphibian, derived from the Greek amphibios meaning “living a double life,” reflects this dual life strategy—though some species are permanent land dwellers, while other species have a completely aquatic mode of existence.

More than 6,500 species of living amphibians are known. First appearing about 340 million years ago during the Middle Mississippian Epoch, they were one of the earliest groups to diverge from ancestral fish-tetrapod stock during the evolution of animals from strictly aquatic forms to terrestrial types. Today amphibians are represented by frogs and toads (order Anura), newts and salamanders (order Caudata), and caecilians (order Gymnophiona). These three orders of living amphibians are thought to derive from a single radiation of ancient amphibians, and although strikingly different in body form, they are probably the closest relatives to one another. As a group, the three orders make up subclass Lissamphibia. Neither the lissamphibians nor any of the extinct groups of amphibians were the ancestors of the group of tetrapods that gave rise to reptiles. Though some aspects of the biology and anatomy of the various amphibian groups might demonstrate features possessed by reptilian ancestors, amphibians are not the intermediate step in the evolution of reptiles from fishes.

Modern amphibians are united by several unique traits. They typically have a moist skin and rely heavily on cutaneous (skin-surface) respiration. They possess a double-channeled hearing system, green rods in their retinas to discriminate hues, and pedicellate (two-part) teeth. Some of these traits may have also existed in extinct groups.

Members of the three extant orders differ markedly in their structural appearance. Frogs and toads are tailless and somewhat squat with long, powerful hind limbs modified for leaping. In contrast, caecilians are limbless, wormlike, and highly adapted for a burrowing existence. Salamanders and newts have tails and two pairs of limbs of roughly the same size; however, they are somewhat less specialized in body form than the other two orders.

Many amphibians are obligate breeders in standing water. Eggs are laid in water, and the developing larvae are essentially free-living embryos; they must find their own food, escape predators, and perform other life functions while they continue to develop. As the larvae complete their embryonic development, they adopt an adult body plan that allows them to leave aquatic habitats for terrestrial ones. Even though this metamorphosis from aquatic to terrestrial life occurs in members of all three amphibian groups, there are many variants, and some taxa bear their young alive. Indeed, the roughly 6,200 living species of amphibians display more evolutionary experiments in reproductive mode than any other vertebrate group. Some taxa have aquatic eggs and larvae, whereas others embed their eggs in the skin on the back of the female; these eggs hatch as tadpoles or miniature frogs. In other groups, the young develop within the oviduct, with the embryos feeding on the wall of the oviduct. In some species, eggs develop within the female’s stomach. http://www.britannica.com/EBchecked/topic/21445/amphibian

Phylum Echinodermata

Echinoderms (Phylum Echinodermata) are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 70,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are also the largest phylum that has no freshwater or terrestrial representatives.

Anatomy and physiology

Echinoderms evolved from animals with bilateral symmetry. Although adult echinoderms possess pentaradial, or five-sided, symmetry, echinoderm larvae are ciliated, free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates. Later, the left side of the body grows at the expense of the right side, which is eventually absorbed. The left side then grows in a pentaradially symmetric fashion, in which the body is arranged in five parts around a central axis. Echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life, even if they have secondary bilateral symmetry. Many crinoids and some seastars exhibit symmetry in multiples of the basic five, with seastars such as Helicoilaster known to possess up to 50 arms, and the sea-lily Comanthina schlegelii boasting 200.

They have a few important aspects in common. They have bony ossicles in their body. They have a water-vascular system which pumps water through the madroporite. They also have small jaws that are supported by the water-vascular system. And they have tube feet which they use to attach to objects, for protection, as well as to obtain food. They have radial symmetry and most can regenerate lost limbs.

The following classes are types of echinoderms:

(1)   Class Asteroidea--Starfish or Sea Stars (Six-rayed Starfish--Leptasterias hexactis)--sea stars have fairly developed senses of smell, touch, and taste. They also can respond to the presence of light. They normally eat small prey whole, but they have to extrude their stomachs to digest larger prey outside their bodies. Sometimes, sea stars will use their tube feet to help pry open bivalves, and then they will slip their stomachs in between the two shells. 

(2)   Class Ophiuroidea--Brittle Stars (Daisy Brittle Star--Ophiopholis aculeata)
Another picture of a Brittle Star (*)--found in all oceans (but mainly in the tropics). The group includes about 2000 species, varying in color. They eat decaying matter and microscopic organisms that are found on soft muddy bottoms.

(3)   Class Echinoidea

 Sea Urchins--they locomote using short to long, movable spines. Between their spines are small, pincerlike organs calledpedicellariae which they use to clean and defend themselves. The pedicellariae also contain a powerful toxin.

 

(4)   Class Crinoidea--Feather Stars (Florometra serratissima)--feather stars will swim if they are disturbed.

(5)   Class Holothuroidea--Sea Cucumbers


Class Chondrichthyes

            It contains the cartilaginous fishes, those that have a skeleton of cartilage rather than bone. This includes all sharks, skates and rays. They also have five to seven gill slits on each side of the body. Sharks and rays reproduce by passing sperm from the male to the female, the male using modified fins called claspers. Some species produce large egg cases (usually those that live on the bottom) whilst others produce live young (usually those that swim in the water column) (http://www.woodbridge.tased.edu.au/mdc/Species%20Register/class_chondrichthyes.htm).

Taxonomy

Nelson's 2006 Fishes of the World arranges the class as follows:

§  Subclass Elasmobranchii

§  Order Plesioselachus

§  Order Squatinactiformes

§  Order Protacrodontiformes

§  Infraclass Cladoselachimorpha

§  Order Cladoselachiformes

§  Infraclass Xenacanthimorpha

§  Order Xenacanthiformes

§  Infraclass Euselachii (sharks and rays)

§  Order Ctenacanthiformes

§  Division Hybodonta

§  Order Hybodontiformes

§  Division Neoselachii

§  Subdivision Selachii (modern sharks)

§  Superorder Galeomorphi

§  Order Heterodontiformes (bullhead sharks)

§  Order Orectolobiformes (carpet sharks)

§  Order Lamniformes (mackerel sharks)

§  Order Carcharhiniformes (ground sharks)

§  Superorder Squalomorphi

§  Order Hexanchiformes (frilled and cow sharks)

§  Order Echinorhiniformes (bramble sharks)

§  Order Squaliformes (dogfish sharks)

§  †Order Protospinaciformes

§  Order Squatiniformes (angel sharks)

§  Order Pristiophoriformes (sawsharks)

§  Subdivision Batoidea (rays)

§  Order Torpediniformes (electric rays)

§  Order Pristiformes (sawfishes)

§  Order Rajiformes (skates and guitarfishes)

§  Order Myliobatiformes (stingrays and relatives)

§  Subclass Holocephali

§  Superorder Paraselachimorpha

§  Order Orodontiformes

§  Order Petalodontiformes

§  Order Helodontiformes

§  Order Iniopterygiformes

§  Order Debeeriiformes

§  Order Eugeneodontiformes*

§  Superorder Holocephalimorpha

§  Order Psammodontiformes*

§  Order Copodontiformes

§  Order Squalorajiformes

§  Order Chondrenchelyiformes

§  Order Menaspiformes

§  Order Coliodontiformes

§  Order Chimaeriformes (chimaeras)

Class Osteichthyes 

It also called bony fish, are a taxonomic group of fish that have bones, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.

Scientific classification

Kingdom:

Animalia

Phylum:

Chordata

clade:

Craniata

Subphylum:

Vertebrata

Infraphylum:

Gnathostomata

Superclass*:

Osteichthyes
Huxley, 1880

Classes

Actinopterygii
Sarcopterygii

Insect

Michael Fogden/Bruce Coleman Inc.Insect, common name given to any animal of a class belonging to the arthropod phylum. The insects are the largest class in the animal world, outnumbering all other animals. At least 800,000 species have been described, and entomologists believe that as many or more remain to be discovered. The class is distributed throughout the world from the polar regions to the tropics and is found on land, in fresh and salt water, and in salt lakes and hot springs. The insects reach their greatest number and variety, however, in the tropics. In size, the insects also exhibit great variation. Some small parasitic insects are less than 0.025 cm (less than 0.01 in) in length when fully grown, whereas at least one fossilized species related to the modern dragonflies is known to have had a wingspread of more than 60 cm (24 in). The largest insects today are certain stick insects about 30 cm (about 12 in) long and certain moths with wingspans of about 30 cm (about 12 in).Insects also are the most highly developed class of invertebrate animals, with the exception of some mollusks. Insects such as the bees, ants, and termites have elaborate social structures in which the various forms of activity necessary for the feeding, shelter, and reproduction of the colony are divided among individuals especially adapted for the various activities. Also, most insects achieve maturity by metamorphosis rather than by direct growth. In most species, the individual passes through at least two distinct and dissimilar stages before reaching its adult form.

In their living and feeding habits, the insects exhibit extreme variations. Nowhere is this more apparent than in the life cycle of various species. Thus the so-called 17-year locust matures over a period of 13 to 17 years. The ordinary house fly can reach maturity in about ten days, and certain parasitic wasps reach their mature form seven days after the eggs have been laid. In general the insects are very precisely adapted to the environments in which they live, and many species depend on a single variety of plant, usually feeding on one specific portion of the plant such as the leaves, stem, flowers, or roots. The relationship between insect and plant is frequently a necessary one for the growth and reproduction of the plant, as with plants that depend on insects for pollination. A number of insect species do not feed on living plants but act as scavengers. Some of these species live on decaying vegetable matter and others on dung or the carcasses of animals. The activities of the scavenger insects hasten the decomposition of all kinds of dead organic material.

Certain insects also exhibit predation or parasitism, either feeding on other insects or existing on or within the bodies of insect or other animal hosts. Parasitic insects are sometimes parasitic upon parasitic insects, a phenomenon known as hyperparasitism. In a few instances an insect may be parasitic upon a secondary parasite. A few species of insects, although not strictly parasitic, live at the expense of other insects, with whom they associate closely. An example of this form of relationship is that of the wax moth, which lives in the hives of bees and feeds on the comb that the bees produce. Sometimes the relation between two species is symbiotic. Thus ant colonies provide food for certain beetles that live with them, and in return the ants consume fluids that have been secreted by the beetles.

Social Insects 
One of the most interesting forms of insect behavior is exhibited by the social insects, which, unlike the majority of insect species, live in organized groups. The social insects include about 800 species of wasps, 500 species of bees, and the ants and termites. Characteristically an insect society is formed of a parent or parents and a large number of offspring. The individual members of the society are divided into groups, each having a specialized function and often exhibiting markedly different bodily structures. For discussion of the organization of typical insect societies, see articles on the insects mentioned above.


Dorling KindersleyAnatomy 
Although the superficial appearance of insects is extremely varied, certain characteristics of their anatomy are common to the entire class. All mature insects have bodies composed of three parts: head, thorax, and abdomen (the abdomen and thorax are not always differentiated in larvae). Each of these parts is composed of a number of segments. The head is made up of several segments, usually so fused they are scarcely differentiated. On the head are two antennae; a pair of jaws, or mandibles; a pair of auxiliary jaws, or maxillae, that in turn bears a pair of palps; and a fused second pair of accessory jaws, the labium, that also bears a pair of palps. The antennae, usually attached to the anterior part of the head, are segmented. In some insects, the antennae carry organs of smell as well as organs of touch. The mandibles are large, heavy jaws on either side of the mouth. They close horizontally and are used for grasping food and crushing it. The maxillae, or inner jaws, are lighter in structure. The mouths of many insects are adapted for piercing and sucking rather than for biting. The eyes of the insect are also situated on the head.All insects have three pairs of legs, each pair growing from a different part of the thorax, called, from front to back, the prothorax, the mesothorax, and the metathorax. Many larvae have, in addition, several pairs of leglike appendages called struts, or prolegs. The forms of the legs vary, depending on their uses, but all insect legs are made up of five parts. In winged insects, the wings, usually four in number, grow from the thorax between the mesothorax and the metathorax. The upper and lower membranes of the wings cover a network of sclerotized tubes, called veins, that stiffen the wing. The pattern of veins of the wings is characteristic of most insect species and is extensively used by entomologists as a basis for classification.

Insect abdomens usually have 10 or 11 clearly defined segments. In all cases the anal opening is located on the last segment; in some species, such as the mayflies, a pair of feelers, called cerci, is also present on this segment. The abdomen is devoid of legs. In female insects, it contains the egg-laying organ, or ovipositor, which may be modified into a sting, saw, or drill for depositing the eggs in the bodies of plants or animals. Insect sexual organs arise from the eighth and ninth segments of the abdomen.

Insects have an external rather than an internal skeleton; this exoskeleton is a rough integument formed by the hardening of the outer layer of the body through impregnation with pigments and polymerization of proteins, a process known as sclerotization. The exoskeleton at the joints does not become sclerotized and therefore remains flexible.

Flight 
Most insects possess wings during at least part of their life cycles. Insect wings are large folds in the exoskeleton composed of two sheets of cuticle permeated with stiff supportive veins. The wings are powered by two sets of muscles that independently drive the upstroke and downstroke of the wing movement. The frequency of wingbeats ranges from 4 beats per second in butterflies to nearly 1000 beats per second in some gnats.

Insect wings not only move up and down but they also move forward and backward in an ellipse or figure eight pattern that provides both lift and thrust. Given their shape, speed, and stroke pattern, it has never been clearly understood how insect wings can generate enough lift to sustain flight. Recently scientists discovered that insects generate a vortex, or spiral air motion, along the leading edge of their wings. This vortex flows out toward the wing tip in widening spirals. The whirling cylinder of air above the insect provides the extra lift that makes flight possible.

Respiration 
Certain species of insects breathe through the body wall, by diffusion, but in general the respiratory system of members of this class consists of a network of tubes, or tracheae, that carry air throughout the body to smaller tubelets or tracheoles with which all the organs of the body are supplied. In the tracheoles the oxygen from the air diffuses into the bloodstream, and carbon dioxide from the blood diffuses into the air. The exterior openings of the tracheae are called spiracles. The spiracles are situated on the sides of the insect and are usually 20 in number (10 pairs), 4 on the thorax and 16 on the abdomen. Some water-breathing insects have gill-like structures.

Circulation 
The circulatory system of insects is simple. The entire body cavity is filled with blood that is kept in circulation by means of a simple heart. This heart is a tube, open at both ends, that runs the entire length of the body under the exoskeleton along the back of the insect. The walls of the heart can contract to force the blood forward through the heart and out into the body cavity.


The digestive tract of most insects is divided into the foregut, the midgut (or stomach), and the hindgut. In the foregut, a food passage, or gullet, from the mouth is followed by a crop and a proventriculus. The crop serves as a storage space for food. Salivary glands open into the gullet, and their secretions are mixed with the food during mastication. Digestion takes place primarily in the midgut, and the products are absorbed in the midgut and the hindgut. The food waste passes to the hindgut, or intestine, for elimination. Connected to the forepart of the hindgut are a large number of small tubes, called the Malpighian tubules, that float in the blood of the body cavity. Waste matter in the blood passes through the walls of these tubes and into the hindgut, from which it is eliminated from the body of the insect. 

Echinoderms 

Characteristics of Echinoderms are characterized by radial symmetry, several arms (5 or more, mostly grouped 2 left - 1 middle - 2 right) radiating from a central body (= pentamerous). The body actually consists of five equal segments, each containing a duplicate set of various internal organs. They have no heart, brain, nor eyes, but some brittle stars seem to have light sensitive parts on their arms. Their mouth is situated on the underside and their anus on top (except feather stars, sea cucumbers and some urchins).

Echinoderms have tentacle-like structures called tube feet with suction pads situated at their extremities. These tube feet are hydraulically controlled by a remarkable vascular system. This system supplies water through canals of small muscular tubes to the tube feet (= ambulacral feet). As the tube feet press against a moving object, water is withdrawn from them, resulting in a suction effect. When water returns to the canals, suction is released. The resulting locomotion is generally very slow.

Ecology and range of EchinodermsEchinoderms are exclusively marine. They occur in various habitats from the intertidal zone down to the bottom of the deep sea trenches and from sand to rubble to coral reefs and in cold and tropical seas.

  Behavior of EchinodermsSome echinoderms are carnivorous (for example starfish) others are detritus foragers (for example some sea cucumbers) or planktonic feeders (for example basket stars).

Reproduction is carried out by the release of sperm and eggs into the water. Most species produce pelagic (= free floating) planktonic larvae which feed on plankton. These larvae are bilaterally symmetrical, unlike their parents (illustration of a larvae of a sea star below). When they settle to the bottom they change to the typical echinoderm features.



Echinoderms can regenerate missing limbs, arms, spines - even intestines (for example sea cucumbers). Some brittle stars and sea stars can reproduce asexually by breaking a ray or arm or by deliberately splitting the body in half. Each half then becomes a whole new animal.

Echinoderms are protected through their spiny skins and spines. But they are still preyed upon by shells (like the triton shell), some fish (like the trigger fish), crabs and shrimps and by other echinoderms like starfish which are carnivorous. Many echinoderms only show themselves at night (= nocturnal), therefore reducing the threat from the day time predators.

Echinoderms serve as hosts to a large variety of symbiotic organisms including shrimps, crabs, worms, snails and even fishes.



Sea stars (starfish)(Asteroidea)

 Characteristics of sea stars (or starfish)Sea stars are characterized by radial symmetry, several arms (5 or multiplied by 5) radiating from a central body. Mouth and anus are close together on the underside, the anus is at the center of the disc together with the water intake (madreporite). The upper surface is often very colorful. Minute pincer-like structures called pedicellaria are present. These structures ensure that the surface of the arms stay free from algae. The underside is often a lighter color.

There are a few starfish that have 6 or 7 arms, for example Echinaster luzonicus or Protoreaster, some even more like the elven-armed sea star (Coscinasterias calamaria). Others normally have 5 arms but now have more arms, because after an injury an arm divided and grew into two arms.

Ecology and range or sea starsThe starfish lives everywhere in the coral reef and on sand or rocks.

Behavior of sea starsRegeneration
The ability of an organism to grow a body part that has been lost

Autotomy 
The spontaneous self amputation of an appendage when the organism is injured or under attack. The autotomized part is usually regenerated.

Budding
Is asexual reproduction in which an outgrowth on the parent organism breaks off to form a new individual

Fission
Self-division into two parts, each of which then becomes a separate and independent organisms (asexual reproduction)


 The majority of sea stars are carnivorous and feed on sponges, bryozoans, ascidians and molluscs. Other starfishes are detritus feeders (detritus = organically enriched film that covers rocks) or scavengers. Some starfish are specialized feeders, for example the crown-of-thorns that feeds on life coral polyps.

Starfish have no hard mouth parts to help them capture prey. The stomach is extruded over the prey, thus surrounding the soft parts with the digestive organs. Digestive juices are secreted and the tissue of the prey liquefied. The digested food mass, together with the stomach is then sucked back in. This method can be observed, if you turn around a starfish, that sits on prey or sand - you will see the stomach retreating.

Starfish are well known for their powers of regeneration. A complete new animal can grow from a small fragment such as a arm. In some species (Linckia multifora and Echinaster luzonicus) one of the arms will virtually pull itself away, regenerates and forms a new animal. Autotomy (self amputation) usually is a protective function, losing the body part to escape a predator rather than being eaten. But here it serves as a form of asexual reproduction. In other species of sea stars (Allostichaster polyplax and Coscinasterias calamaria) the body is broken into unequal parts (= fission) then the missing limbs regenerate.
The crown-of-thorns (Acanthaster planci) is one of the largest and the most venomous starfishes. It can reach 50 cm diameter and has numerous (10 to 20) spiny arms with formidable thorn like toxic spines. Don't touch them! A species of small cardinalfishes (Siphamia fuscolineata) and a commersal shrimp (Perliclimenes soror) live among those spines. The crown-of-thorns feed on live coral polyps. They "graze" the corals which are left behind white and dead. Their predators are the giant triton shell (Charonia tritonis) and some puffer fish. Scientist have also found out, that some crown of thorns are deterred from eating the coral polyps by the small crabs living among the coral branches (Trapezia sp). These crabs defend their coral host by breaking them off at the pedicellaria. Other small crabs (Tetralia sp) only pinch the tube feets of the starfish. Crown of thorns prefer corals, that are not hosts to these crabs.

The cushion star (Culcita nouvaeguineae) doesn't look like a starfish at all, more like a large sea urchin without spines. Its pentagonal appearance gives only the slightest indication that this organism is related to other starfish.Characteristics of sea cucumbersUnlike other echinoderms, holothurians don't have a distinct radial symmetry but are bilateral (distinct dorsal and ventral side). Holothurians are also called sea cucumbers. As their name suggests, they are cucumber shaped with an elongated, muscular, flexible body with a mouth at one end and the anus at the other. Around the mouth there is a number of tentacles (modified tube feet) used in food collecting. Sea cucumbers come in many sizes, from small species only a few centimeter in length to long snakelike animals which may stretch up to 2 meter!

Ecology and range of sea cucumbersRubble, rocks and sand. Also seen on some sponges in large aggregations.

Behavior of sea cucumbersMost species feed on the rich organic film coating sandy surfaces. The crawl over the bottom ingesting sand. The edible particles (organic matter such as plankton, foraminifera and bacteria) are extracted when passing through their digestive tract and the processed sand is expelled from the anus (as worm-like excrements).

Sea cucumbers move by means of tube feet which extend in rows from the underside of the body. The tentacles surrounding the mouth are actually tube feet that have been modified for feeding.

Other holothurians feed on current-borne zooplankton. They bury in sand extruding their featherlike tentacles (Pseudocolochirus violaceus, Neothyondium magnum or Pentacta crassa). The tentacles have the same shape as soft corals or some anenemones. Large congregations of some small species are found on sponges. They apparently feed on substances secreted by the sponges as well as detritus from the surface.

Some species of holothurians have separate sexes others are hermaphrodites. The sea cucumbers hold on to exposed rocks or corals, raise their body to a upright position, rock back and forth and release the sperm and eggs into the sea.

 Sea cucumbers have a remarkable capacity for regenerating their body parts. When attacked they shed a sticky thread like structure which is actually parts of their guts. The so called Cuverian threads are toxic (the poison is called holothurin) and can dissuade many potential predators. These structures quickly regenerate. (see photos below)

Pearlfish(Carapidae)

Encheliophis homei and mourlani / Onuxodon margaritiferae

 Holothurians host a variety of symbiotic organisms: crabs, shrimps, worms and even a very unusual fish. The pearlfish (Encheliophis homei and mourlani / Onuxodon margaritiferae) has a long slender, transparent body and lives in the gut cavity of the sea cucumber (Boshida argus, Thelanota ananas, Stichopus chloronotus). They also inhabit some starfish as well as pearl oyster shells. The fish leaves and enters (tail first) through the holothurian's anus. They probably feed on the gonads and other tissues of its host. It is said to leave at night to feed on small fishes and shrimps. Sea cucumbers are used in Asia as a base for soups.


http://www.starfish.ch/reef/echinoderms.html.

SEGMENTED WORMS       

Segmented WormsSegmented worms (phylum Annelida) are so named because of their elongated, more or less cylindrical bodies divided by grooves into a series of ringlike segments. Typically, the external grooves correspond to internal partitions called septa, which divide the internal body space into a series of compartments. Perhaps the most familiar examples of segmented worms are the common earthworms or night crawlers, and the freshwater leeches. Actually, the more numerous and typical members of the phylum are marine, crawling or hiding under rocks, or living in burrows, or in tubes, or in the sediment.There are approximately 15,000 living species of annelids, placed in three major classes: the Polychaeta (mostly marine), the Oligochaeta (mostly terrestrial), and the Hirudinea (mostly freshwater).
 
Polychaetes are either "errant"—moving and feeding actively, or "sedentary"—with a passive lifestyle. The basic body plan of an errant form is illustrated by the sandworm Nereis. The anterior end of Nereis is specialized to form a "head," possessing two pairs of eyes and several pairs of sensory appendages. The remainder of the body consists of a large number (100 or more) of similar segments, each with a pair of distinct lateral appendages called parapodia. The parapodium is muscular, highly mobile, and divided into two lobes, an upper, or dorsal, "notopodium," and a lower, or ventral "neuropodium." Each lobe bears a bundle of bristles, or setae. The setae, made of a substance called chitin, are used in crawling or in swimming. Nereis is a carnivore. Its food consists of small live organisms, or fragments of dead organisms, which it grasps by means of a pair of powerful jaws located at the tip of an eversible muscular pharynx. The food is ground up and digested as it passes through successive parts of the straight, tubular gut. The undigested residue is discarded through the anus located at the posterior end.

Most other body systems are arranged on a "segmental plan," which means that structures performing a particular body function are repeated in each segment. Thus, for excretion each segment contains a pair of coiled, ciliated tubes called nephridia. At one end the nephridial tube opens into the spacious cavity (called coelom) between the body wall and the gut; at the other end it opens to the outside. There is a well developed circulatory system. The blood, which is red in color due to the presence of hemoglobin, circulates in blood vessels. Gas exchange occurs between blood and sea water across the thin, leaf-like lobes of the parapodia.

Each body segment also has a pair of nerve ganglia and three or four pairs of nerves for receiving sensory input and coordinating muscular activity. Ganglia in successive segments are connected by means of a pair of longitudinal nerve cords, so that nerve impulses can be transmitted back and forth between each segment and the "cerebral ganglion" or "brain" located in the head. Sexes are separate, although no external characteristics distinguish males from females.



Read more: Segmented Worms - Body, Leeches, Polychaetes, and Blood - JRank Articles http://science.jrank.org/pages/6062/Segmented-Worms.html#ixzz1pnIAahYW   

 Mollusca

 After the Arthropods the Molluscs are the most successful of the animal phyla in terms of numbers of species. There are about 110,000 species known to science most of which are marine. They occupy a vast range of habitats however both aquatic and terrestrial, from the arctic seas to small tropical streams and from valleys to mountainsides 7,000 metres high, there are a few adapted to live in deserts and some are parasitic.    


They also exhibit an enormous range in size, from species which are almost microscopic to the largest of all invertebrates the giant squid which can weighs 270 kg and measures up to 12 metres long in the body, with tentacles as much as another 50 metres in length. Many species are common and many more a beautiful. Most species secrete a shell of some sort, these shells are long lasting and have been collected by human beings for thousands of years, some of these shells, and the pearls which come from oysters, which are also molluscs may be among the earliest forms of money.

Etymology:- From the Latin Molluscus meaning soft of body.


Characteristics of Mollusca:- 
1)Bilaterally symmetrical. 
2)Body has more than two cell layers, tissues and organs. 
3)Body without cavity. 
4)Body possesses a through gut with mouth and anus.
5)Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. 
6)Has a nervous system with a circum-oesophagal ring, ganglia and paired nerve chords. 
7)Has an open circulatory system with a heart and an aorta. 
8)Has gaseous exchange organs called ctenidial gills. 
9)Has a pair of kidneys. 
10)Reproduction normally sexual and gonochoristic. 
11)Feed a wide range of material.

Adapted from  http://www.earthlife.net/inverts/mollusca.html
   designed and written by Mr Gordon Ramel 

Ecology can be defined as  the scientific study of interactions that determine the distribution & abundance of organisms.  Since this is a course in animal ecology, we will focus on animals, which we will define fairly generally as organisms that can move around during some stage of their life and that must feed on other organisms or their products.

Let's explain the terms in the definition of ecology.

Distribution refers to where organisms are found.  We can study distribution on different scales:

• where found geographically
• where found in terms of habitat
• how distributed spatially within habitat

Abundance refers to how many organisms occur.  We can ask different questions about abundance:

• does a species occur in many habitats?  If so, it will appear abundant on a large scale -- we will encounter it in many places.
• are there large numbers of individuals of a species in a habitat where it occurs?  If so, a species may be rare or abundant on a large scale, but in certain localities it will be abundant.
• we can also look at abundance in terms of numbers of species, rather than in terms of individuals of a single species.  We can ask whether an area has many different species or only a few species.

Interactions refer to the relationships between an organism or species and aspects of its environment.  The environment refers to the surroundings of an organism or species, and is generally considered to consist of two categories of factors:

• biotic factors refer to other organisms that interact with an organism or species, or the organic products of those organisms.  Examples of biotic factors include:
• the species that produce the food eaten by an organism
• species that feed on and harm the organism, including:
• predators: species that kill and eat their prey and have no long term interaction with them
• parasites: species that live on or in their host over a long period of time and harm, but are unlikely to directly kill, the host
• parasitoids: species whose eggs are laid on the host (typically on the larval stages of insect hosts) and which then develop in or on the host, harming it as parasites do, but that eventually grow large and kill the host
• brood parasites: species (typically birds) that lay eggs in the nests of their host species.  The hosts care for these young and their own young are usually harmed or killed
• iterspecific competitors of the organism -- other species that use the same resources and deplete supplies of those resources so that they negatively impact an organism
• mutualists -- species whose presence is helpful or essential to the organism, and who are helped by the organism
• members of same species, through:
• intraspecific competition: use of same resources, so members of same species affect each other negatively
• behavioral interactions
• abiotic factors refer to non living aspects of the environment that affect an organism, such as oxygen, water, pH, salinity,...

Note that biotic and abiotic factors interact.  For example, plants (biotic factors) in an environment tend to increase the amount of oxygen (an abiotic factor.) The above explanations of distribution, abundance, and interactions should indicate that we can study ecology on a various different levels.  The main levels studied by ecologists are:
 

• individuals.  We can consider how individuals are affected by the environment; this can determine whether they can survive (which will affect their distribution) and how well they reproduce (which will affect their abundance.)  We will spend some time early in this course looking at how the physiology of individual organisms relates to their survival and reproduction in the environments where they occur.
• populations.  A population is a group of organisms of the same species within a defined area.  We can look at the factors that determine how large a population grows,  that regulate it at a certain size, or that cause population size to fluctuate.  A large part of this course will be spent studying populations
• communities.  A community usually refers to all the organisms within an area.  We can also talk about a community of some type of organism, such as the community of rodents in a field in West Tennessee.  We will look at factors affecting the numbers of species in communities later in this course.
• ecosystems.  An ecosystem refers to all the organisms within an area and the abiotic factors that affect it.  We will not consider ecosystems very much in this course; ecosystem interactions are strongly dependent on plants so they often fall outside the area of animal ecology, although you should all realize that animals are part of an entire ecosystem and interact with the entire ecosystem.

The final aspect of the definition of ecology that we started with is that ecology is a scientific study.  Scientific study means using the scientific method, which is discussed below.  It is an important part of the definition of ecology because it indicates that to study ecology we must be doing the things associated with science -- testing hypothesis with objectively obtained, repeatable data.  It is important to consider this with regard to ecology because we get a lot of information about organisms and their environments in ways that are NOT scientific.  For example, I like birds, and I like to go out birding to see how many different species I can observe in some area or time.  When I'm out birding, I am NOT being an ecologist -- I'm getting information about the natural world but it is biased, not repeatable, not objective.  In contrast, I also study birds, and when I am getting nest success information on a population of meadowlarks I try my best to do it in a way that IS repeatable and objective; while doing that, I am being an ecologist.

The Scientific Method involves the following steps:

1. ask questions about the natural world
2. develop possible explanations, answers to these questions, that can be tested by doing experiments or taking observations.  An hypothesis is a plausible, testable explanation for some phenomenon observed in the natural world.  It must be consistent with what is already known about the world, and it must be possible to take data in a repeatable, objective manner to test the hypothesis.
3. make predictions: observations or experimental results that we would expect to observe if the hypothesis we are testing is true.
4. take data -- through experimentation and/or observation determine whether we see the predictions that are predicted based on our hypothesis.  These data must be taken in a repeatable way.  Ideally, we take data such that we look at just one factor at a time; this often involves having a control group which we do not manipulate and an experimental group which we manipulate in just one way.
5. evaluate our hypothesis based on the data:
6. if our prediction is NOT met, then our hypothesis must be false
7. if our prediction IS met, then our hypothesis MIGHT be true -- we say it is "supported."  This is a weaker conclusion than we would get if our prediction was not met.  This is because it is always true that there might be some other hypothesis that makes the same prediction as the hypothesis we are testing.  The result of this is that we never know for sure that an hypothesis is true.

While we never know for sure that any hypothesis is true, we can conduct experiments that allow us to say it is very very likely that a hypothesis is true.  To do this, we use a method called strong inference, which involves:

• considering several different hypotheses that might explain the phenomenon we're studying
• develop predictions of the hypotheses that are mutually exclusive -- that is, a prediction of one hypothesis is something that is NOT predicted by the other hypotheses

If we can do this for every hypothesis we, or anyone, can think of, and only support one hypothesis, then we're pretty sure it's true.  It remains possible however that someone smarter will come along and think of another hypothesis that explains all the results just as well as the one we thought was true. Testing hypotheses in ecology can be fairly difficult.  A less formal definition of ecology (don't learn this one for the tests!) is "science under the worst possible conditions."  The main reason for this is that when we are looking at organisms in their environments, they are affected by many factors, and it is hard or impossible to change one without changing others.  It is thus very hard to do a real controlled study in ecology.  Ecologists take different approaches to this problem:

• laboratory studies.  Populations of many species have been grown and studied in laboratory conditions.  The advantage to this approach is that by bringing organisms into the lab, ecologists can reduce the number of factors affecting them and change factors one at a time.  The disadvantage is that the factors that affect a population in the lab may be different from those that really affect it in nature -- by creating a laboratory situation we risk creating a situation so different from nature that what we determine in the lab does not apply in nature.
• field observations.  By observing organisms in different environments, or at different times of the year, we may be able to determine the factors that are really affecting them.  Careful observation of natural communities is the basis for developing hypotheses in ecology.  However, often many different factors vary together so it is difficult to know which really causes any patterns we observe.
• field experiments.  We can sometimes change factors in a field setting to see how they affect the populations we are studying.  These ideally allow us to test our hypotheses in a natural setting so that it is less likely that the factors we study have no real importance to the species than it would be for a laboratory study.  It is hard or impossible, however, to change just one factor at a time in a natural setting.(http://www.utm.edu/departments/biology/rirwin/441_442/441introlec.htm)

   Zoology is the science of studying about the animals. The animal kingdom has fascinated mankind for centuries together. People try and understand the evolution of life, extinction and emergence of species to understand different biological cycles.

         Many scientists have published catalogues of their observation about the existence of animals and plants in deep seas and far-off lands. The exploration of nature still continues.

         Zoology is recorded to have originated from China and Arabia when Al-Jahizz, a famous Afro-Arab scholar wrote a book on animals. Other popular people who have published their observations in the same field are Shen Kuo and Su Song.

         Reports state that scientific zoology began during the 16th century where the spirit of exploration, observation and research took shape. However, it was considered a separate field of study independent of physiology, anatomy and other medical research fields. Initially, this field started manifesting in the universities in Italy before it moved to the Oxford University 50 years later!

         In the year 1651, the popular institution in Europe named Academia Naturae Curiosorum started analyzing, illustrating and describing the structure of animals as well as plants. It was the incorporated by the Royal Society of London after about 11 years. Louis XIV established the Academy of Sciences in Paris. Anatomists and scientists set to work seriously in this field during the end of the eighteenth century.

         The first microscope invented by Leeuwenhoek created a huge revolution in the field of Zoology. During the nineteenth century, the microscope was made better with improved features to help establish the cell theory.